Ring & pinion question ??

[jonabalco]

Once again I am going to ask people who have been there done that !!
I'm currently building a 68 GMC short bed Here's what I have !! I have taken the 305 V6 out and dropped a 4 bolt main 350 about 400 HP I have kept the sm 4speed Muncie tranny it's the tranny where 1st is kind of a granny gear .... The rear gears are currently 3:54 i'm looking to get a little more speed out of it ... Am I better with a set of 3:28 or going with a set of
4:09 gears please let me know any help is GREATLY appreciated !!!

[jeffahart]

I would keep the gears you have and make adjustments via tire size. I liked 4.10 when I had it with my sm465. But I also ran 33" tires. I now have 4.56 and plan to up 35" to 37" tires. I like lower gears in a truck with the truck transmission. If you plan on hauling anything up any hills then definitely don't go any higher in the gears. You will dog up hills.

Here's another thing. When you are on the highway cruising see where the engine is comfortable. Every engine has a sweet spot RPM wise that you will feel the engine is comfortable to cruise at. Use that to gauge where you want your speed to be in relation your RPM

[jonabalco]

well I don't plan on really hauling any thing I just don't want to top out at 75 MPH I have taken the old 16's off cause of rust and don't really know what shape the rims are in till I get them sand blasted ... I got a FREE set of 15's that are alum. so that's what i'm running now ... So if I put 4:10's will it give me a little higher speed range over the 3:54 ??? I know there is probly a formula out there but I figured I would try here 1st .. thanks jeff for any info !!!

[Wrenchbender Ret]

The 4:10 will give you lower speed. For better highway gearing go for the 3.28. The V-6 is a high torque engine with lower RPM. It will pull it good.

[jeffahart]

He DXed the 6 and is running a 350. Believe me, pick your tires and run the truck highway for awhile; and then decide on your gears. Nobody can answer your question here. You have to run it, then decide... or let your engine decide based on cruising RPM or towing or whatever your most important application and how you feel about the performance.

[Stocker]

Originally Posted by jonabalco

The rear gears are currently 3:54 i'm looking to get a little more speed out of it ... Am I better with a set of 3:28 or going with a set of 4:09 gears

Sounds like you're looking for higher potential top speed, not faster acceleration. If that's the case, higher gears (such as your example of 3.28:1) is the direction you should go. The engine will turn fewer RPM at a given speed, so if it has enough grunt, you'll be able to go faster.

If you went instead with lower gears (such as your example of 4.09:1), the truck will accelerate more quickly, but the engine will be turning more RPM at a given speed, so your potential top speed will be lower.

[jonabalco]

thanks that what i'm looking for not so much as to go 0 to 100 in 10 seconds just don't want the truck to top out at 75 mph and 5k in rpm's !! I do think I might go with a little taller tire and drive it around a bit with the 3:54:1 ration and if not good enough go to a 3:28:1 ..... I should have it ready in a month and let u guys know how it goes !! TY for all the advice !!!